Method for producing an attachment element

ABSTRACT

The invention relates to a method for producing an attachment element (R) comprising a shaft ( 100 ) having a first end provided with a head ( 200 ) and a second end that is intended to be deformed in order to form a button ( 300 ) providing a bearing surface opposite the surface formed by the head ( 200 ), said shaft ( 100 ) having a nominal diameter (D). The method is characterised in that the element is sized such that the minimum length (L) of the shaft ( 100 ) to be deformed to form the button ( 300 ) is no less than  1.25  times the nominal diameter (D) of the shaft ( 100 ). The invention is suitable for use in the production of attachment elements, such as rivets.

FIELD OF THE INVENTION

The present invention relates to the field of fastening elements such asrivets and particularly to adaptations for enhancing the mechanicalfeatures thereof.

DESCRIPTION OF THE PRIOR ART

There are a plurality of rivets and manufacturing methods in the priorart liable to have the mechanical features sought. Nonetheless, thefatigue and tearing strength criteria applicable to rivets areincreasingly stringent.

However, while one solution to meet these criteria lies in increasingthe rivet dimensions, such an increase involves the drawback of theappearance of cracks.

DESCRIPTION OF THE INVENTION

For this reason, the applicant conducted research aimed at providing asolution for the most stringent criteria in respect of the fatigue andtearing strength criteria, on one hand, and at solving the technicalproblem of the appearance of cracks, on the other.

This research resulted in the design of a method for manufacturing,using a metal wire, a fastening element such as that having a shankwherein a first end is equipped with a head, the second end beingintended to be deformed to act as a knob forming a bearing surface to bepositioned facing that formed by the head, said shank having a nominaldiameter. This fastening element is designed such that the minimumlength of the shank intended to be deformed to act as the knob is notless than 1.25 times the nominal diameter of the shank.

The invention is remarkable in that it consists of

-   -   obtaining, for the metal wire, a material grain adopting a size        of 6 or finer according to the criteria defined by the ASTM E        112 standard,    -   performing, on said wire, a work-hardening step wherein the rate        is greater than 30%, and    -   designing said element such that the minimum diameter of the        knob obtained after deforming the shank is greater than 1.75        times the nominal diameter of the shank.

These features ensure that a knob and thus a fastening element having asatisfactory fatigue strength are obtained.

Obtaining a finer grain requires additional working operations on thematerial, rendering the wire production method longer and more costly.In this way, for example, the proposed work-hardening should beperformed in a plurality of steps. Furthermore, a suitable heattreatment should be used.

A person skilled in the art would not turn to such a solution requiringmore operations and control of these base wire manufacturing operationsbefore producing the rivet. A person skilled in the art facing the sametechnical problem would prefer to purchase a more expensive materialsuch as titanium to obtain a fastener having the same features.

According to one further particularly advantageous feature of theinvention, the knob obtained after deforming the shank has a maximumthickness equal to 0.45 times the nominal diameter of the shank. Such athickness associated with the diameter defined above makes it possibleto obtain a fastening element meeting fatigue and tearing strengthcriteria.

The invention also relates to the rivet having all or some of thefeatures described above.

In addition to the dimensional and grain features presented by the wireselected for manufacturing the fastening element according to theinvention, further features suitable for obtaining a fastening elementmeeting the criteria without involving the risk of cracking, have alsobeen devised.

Further features of the manufacturing method are particularly based onthe selection of the features of the wire from which the fasteningelement is forged and the constituent materials of said wire, which issubject to a method comprising specific work-hardening steps, and theelement obtained is subject to a quenching step, etc.

This wire is an aluminum alloy wire which, in addition to the aluminum(Al) compound, comprises additional elements such as:

Chromium symbolized by CR, Copper symbolized by CU, Iron symbolized byFE, Magnesium symbolized by MG, Manganese symbolized by MN, Siliconsymbolized by SI, Titanium symbolized by TI, Zinc symbolized by ZN,Zirconium symbolized by ZR, etc. The proportions described below areminimum or maximum percentages of the elements alone or a combination ofelements. These compositions are suitable for taking on the soughtmechanical properties for a fastener while preventing the presence ofcracks particularly due to the copper content. They are also suitablefor conducting the desired work-hardening and thus obtaining the finegrain sought.

In this way, according to one particularly advantageous feature, themanufacturing method according to the invention is remarkable in that itconsists of selecting, for the metal wire from which the fasteningelement is formed, an aluminum alloy wherein the additional elements toaluminum adopt as a percentage the following proportions:

min max CR 0 0.04 CU 2 2.5 FE 0.011 0.14 MG 2.04 2.3 MN 0 0.05 SI 0.020.12 TI 0.02 0.06 ZN 6.1 6.7 ZR 0.08 0.15

According to a further particularly advantageous feature, the methodconsists of selecting, for the metal wire from which the fasteningelement is formed, an aluminum alloy wherein the additional elements toaluminum adopt as a percentage the following proportions:

min max CR 0.05 0.1 CU 2.6 3 FE 0.34 0.5 MG 0.33 0.5 MN 0.1 0.2 SI 0.320.8 TI 0 0.01 ZN 0.1 0.17 FE—MN 0.47 0.68 TI—ZR 0.05 0.15

According to a further particularly advantageous feature, the methodconsists of selecting, for the metal wire from which the fasteningelement is formed, an aluminum alloy wherein the additional elements toaluminum adopt as a percentage the following proportions:

min max CR 0 0.03 CU 3.5 4.3 FE 0.016 0.3 MG 0.43 0.65 MN 0.41 0.63 SI0.21 0.4 TI 0.005 0.08 ZN 0.002 0.04.

The condition of the wire is also the subject of further specificselections. For example, according to one particularly advantageousfeature, the method consists of selecting a wire which does not haveinclusions (isolated nicks, abrasions, pitting, isolated minorinclusions, cold shuts, non-continuous scratches, tool marks, burrs,etc.) greater than 0.15 millimeters in depth. Furthermore, the methodconsists of selecting a wire wherein the depth of longitudinalcontinuous defects does not exceed 40 microns.

A further feature of this method relates to the quenching step.According to a technological choice, the method consists of subjectingsaid element to a cooling step wherein the time for transferring thefastening elements from one medium wherein the temperature is equivalentto that of solution to a medium wherein the temperature is 20 degreesCelsius is less than 5 seconds.

Finally, according to a further feature, the method consists ofsubjecting said element to a quenching step wherein the temperaturevariation during the quenching of the same batch of elements does notexceed 5 degrees Celsius.

According to a further particularly advantageous feature of theinvention, the shank end radius of the fastening element, i.e. theconnecting radius between the cylindrical surface of the shank and theplane surface of the shank end, is proportional to the diameter of theshank itself according to a proportion wherein said radius is equal tothe nominal diameter of the shank divided by a value ranging between 3and 3.5.

A rivet having an association of these features in the manufacturingmethod thereof is suitable not only for meeting fatigue and tearingstrength criteria but also for preventing the presence of cracks.

A further feature helping obtain a crack-free fastener consists ofselecting, from the manufactured fasteners, a fastener wherein the shankparticularly at the part to be deformed, i.e. at the shank end radius,does not have longitudinal continuous defects greater than 40 microns.

It would thus appear that the invention consists of a series of featureselections both upstream from the manufacture of the fastening elementfor example in the choice of the features of the base wire anddownstream, i.e. not only in the final dimensions but also in the finalsurface condition of the fastening element obtained.

The invention thus also relates to the fastening element obtainedaccording to all or some of the features of the method described above.

The fundamental concepts of the invention described above in the mostbasic form thereof, further details and features will emerge moreclearly on reading the following description and with reference to theappended figures, giving as a non-limiting example, an embodiment of afastening element according to the invention.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a schematic drawing of a sectional view of an embodiment of arivet according to the invention fitted in an orifice passing throughtwo parts to be assembled;

FIG. 2 illustrates the assembly produced using the embodiment in FIG. 1.

DESCRIPTION OF PREFERRED EMBODIMENTS

As illustrated in the drawing in FIG. 1, the rivet R is fitted in a holeT passing through two plates P1 and P2 to be assembled. This rivet R hasa shank 100 wherein a first end is equipped with a head 200, the secondend being intended to be deformed to act as a knob 300 (see FIG. 2)forming a bearing surface to be positioned facing that formed by thehead 200, said shank having a nominal diameter D. As illustrated beforedeformation, a portion of the shank 100 of the rivet R projects outsidethe hole T. According to the invention, so as to meet the fatigue andtearing strength criteria, the rivet R is designed such that the minimumshank length L intended to be deformed to act as the knob 300, i.e. theminimum shank length projecting outside the hole T, is equal to 1.25times the nominal diameter D of the shank 100.

According to a further particularly advantageous feature of theinvention, the knob 300 obtained after deforming the shank 100 has amaximum thickness e equal to 0.45 times the nominal diameter D of theshank.

According to a further feature, the minimum diameter d of the knob 300,obtained after deformation, is greater than 1.75 times the nominaldiameter D.

Finally, the shank end radius r is equal to the nominal diameter D ofthe shank divided by a value ranging between 3 and 3.5.

It is understood that the fastening element and the method have beendescribed above and represented for the purposes of disclosure ratherthan limitation. Obviously, various adaptations, modifications andenhancements may be made to the example above, without leaving the scopeof the invention.

1. Method for manufacturing, using a metal wire, a fastening elementsuch as that having a shank wherein a first end is equipped with a head,the second end being intended to be deformed to act as a knob forming abearing surface to be positioned facing that formed by the head, saidshank having a nominal diameter, said element being designed such thatthe minimum length of the shank intended to be deformed to act as theknob is not less than 1.25 times the nominal diameter of the shank,characterized in that it comprises obtaining, for the metal wire, amaterial grain adopting a size of 6 or finer according to the criteriadefined by the ASTM E 112 standard, performing, on said wire, awork-hardening step wherein the rate is greater than 30%, and designingsaid element such that the minimum diameter of the knob obtained afterdeforming the shank is greater than 1.75 times the nominal diameter ofthe shank.
 2. Method according to claim 1, characterized in that itcomprises designing said element such that the knob obtained afterdeforming the shank has a maximum thickness (e) equal to 0.45 times thenominal diameter of the shank.
 3. Method according to claim 1,characterized in that said element comprises a rivet.
 4. Methodaccording to claim 1, characterized in that it comprises selecting, forthe metal wire from which the element is formed, an aluminum alloywherein the additional elements to aluminum adopt as a percentage thefollowing proportions: min max CR 0 0.04 CU 2 2.5 FE 0.011 0.14 MG 2.042.3 MN 0 0.05 SI 0.02 0.12 TI 0.02 0.06 ZN 6.1 6.7 ZR 0.08 0.15.


5. Method according to claim 1, characterized in that it comprisesselecting, for the metal wire from which the fastening element isformed, an aluminum alloy wherein the additional elements to aluminumadopt as a percentage the following proportions: min max CR 0.05 0.1 CU2.6 3 FE 0.34 0.5 MG 0.33 0.5 MN 0.1 0.2 SI 0.32 0.8 TI 0 0.01 ZN 0.10.17 FE—MN 0.47 0.68 TI—ZR 0.05 0.15.


6. Method according to claim 1, characterized in that it comprisesselecting, for the metal wire from which the fastening element isformed, an aluminum alloy wherein the additional elements to aluminumadopt as a percentage the following proportions: min max CR 0 0.03 CU3.5 4.3 FE 0.016 0.3 MG 0.43 0.65 MN 0.41 0.63 SI 0.21 0.4 TI 0.005 0.08ZN 0.002 0.04.


7. Method according to claim 1, characterized in that it comprises ofselecting a wire which does not have inclusions (isolated nicks,abrasions, pitting, isolated minor inclusions, cold shuts,non-continuous scratches, tool marks, burrs, etc.) greater than 0.15millimeters in depth.
 8. Method according to claim 1, characterized inthat it comprises selecting a wire wherein the depth of longitudinalcontinuous defects does not exceed 40 microns.
 9. Method according toclaim 1, characterized in that it comprises subjecting said element to acooling step wherein the time for transferring the fastening elementsfrom one medium wherein the temperature is equivalent to that of thesolution treatment to a medium wherein the temperature is 20 degreesCelsius is less than 5 seconds.
 10. Method according to claim 1,characterized in that it comprises subjecting said element to aquenching step wherein the temperature variation during the quenching ofthe same batch of elements does not exceed 5 degrees Celsius.
 11. Methodaccording to claim 1, characterized in that the fastening element isdesigned such that the shank end radius is proportional to the diameterof the shank itself according to a proportion wherein said radius isequal to the nominal diameter of the shank divided by a value rangingbetween 3 and 3.5.